This proposal investigates the nature of the neural basis of motor behavior, as a special window into higher brain functions. In this investigation, we link sophisticated three-dimensional computergraphic analyses of movement with experiments that allow us to infer underlying motor control processes performed under conditions of failure of specific motor systems. All of the experiments that follow proceed from this unique vantage point, and should mark a significant advance in our understanding of brain function for motor behavior. Five experiments are proposed that investigate performance of patients with damage to three central motor systems of the brain. Neural Basis of Motor Planning and Control Experiment 1-3 study the neural basis of motor planning and control, beginning with the possible breakdown of a motor law, moving to the spatial control of hand trajectories, and finally to underlying brain processes for complex movements. Neural Basis of Motor Equivalence Experiment 4 investigates the neural basis of a process of motor control integral to the production of speech as well as control of the limbs, that of motor equivalence. Interplay Between Linguistic and Motor Behavior Experiment 5 begins the investigation of the interplay between neural control processes for linguistic and for motor behavior, from the study of a motor disorder in deaf signers. These three-dimensional, computergraphic analyses of movement should not only advance our understanding of the neural basis of motor behavior but should also serve as a useful tool in evaluating diseases which affect the motor systems of the brain.